1. Field of the Invention
The present invention relates to an image forming process, an image forming apparatus, an electrophotographic image-receiving sheet, and a color electrophotographic print which can produce an image with high quality equivalent to silver halide photographs.
2. Description of the Related Art
Electrophotography is a process in which a latent electrostatic image is formed on a photoconductor as a result of photoconduction and applying colored charged fine particles (a toner) to the latent electrostatic image by action of electrostatic force to thereby form a visible image (toner image).
In electrophotography, many techniques which specify density and glossiness of images have been proposed. For example, Japanese Patent Application Laid-Open (JP-A) No. 06-67468 proposes an image forming process for producing a fixed image having a specular glossiness at an incident angle of 75 degrees of 40% or more, and an optical density of 2.0 or less.
JP-A No. 09-160315 discloses an image processor having image type identifying means based on a density control signal, and process control means for controlling glossiness based on the image type in order to control the glossiness imagewise.
JP-A No. 11-84719 discloses the relationship among an amount of an attached toner, a density, and glossiness. According to this technique, however, a 60-degree glossiness is low of at most 40, and the glossiness may decrease when a toner having a small average particle diameter is used.
JP-A No. 2001-22118 proposes a color toner for electrophotography having a specified relationship between a toner additive and an image density and exhibiting an image density after image-fixing of 1.2 to 2.0.
JP-A No. 2001-305756 proposes an image forming process in which the glossiness of an electrophotographic photoconductor changes 10% or less during continuous printing.
JP-A No. 2002-55495 discloses an electrophotographic two-component developer comprising a carrier and a toner and having a 60-degree glossiness of 15% or more and an image density of 1.4 or more.
However, these conventional technologies do not achieve high density in terms of an optical density exceeding 2.0 and do not yield satisfactory gloss over the entire densities.
JP-A No. 2001-117279 proposes an image forming process in which a toner particle diameter is 7 μm or less, a toner resin has a weight-average molecular weight (Mw) of 19000 or less and a number-average molecular weight (Mn) of 5000 or less, a 75-degree glossiness in a black area is from 90 to 110 and an optical density is from 1.8 to 2.5. According to this technique, however, a sufficient glossiness over the entire densities (particularly at intermediate densities) is not obtained, although the glossiness in the black area is sufficient.
Some of recording media for use in silver halide photographic printing, pictro printing, thermosensitive color printing, sublimation thermal transfer printing, and other printing systems have a logo on the back side. However, these printing techniques can form an image only on one side (i.e., front side) of a recording medium. In contrast, double-sided printing is generally implemented in electrophotography.
Attempts have been made to improve photographic quality such as imparting gloss in image-forming sheets for high quality electrophotography rich in photographic texture. However, electrophotographic prints having two glossy sides invite significant blocking between image-bearing surfaces and cannot yield high photographic quality on both sides.
Such an electrophotographic image-receiving sheet for electrophotography is generally capable of bearing a high-quality print rich in photographic texture on one side (front side) and exhibits different performance on its back side. To obtain photographic quality, the electrophotographic image-receiving sheet must be properly set in a sheet tray after distinguishing between its front side and back side. If the electrophotographic image-receiving sheet is set inversely in a sheet tray by mistake, an intended high-quality print rich in photographic texture is not obtained, troubles in an electrophotographic apparatus such as defective conveying of the sheet, offset, and dust occur, thus significantly adversely affecting other prints.
According to conventional technologies, media (electrophotographic image-receiving sheets), hardware such as a printer and a postprocessing device, and a toner are not optimized, sufficient glossiness over the entire densities covering bright areas (a white area and a highlight area), areas at intermediate densities, and dark areas (a black area and a shadow area) is not obtained, high image quality equivalent to silver halide photographs (photographic quality in its original meaning) is not achieved, and a printing system that can prevent misloading has not yet been provided.